Underbed thread trimmer for chainstitch sewing machines

ABSTRACT

An underbed thread trimmer for a chainstitch sewing machine in which a pair of ledger blades are adjustably mounted on the machine bed, a thread catcher being carried pivotably by said bed having needle thread and looper thread catching hooks and a pair of cutting edges cooperable with respective ones of said ledger blades. Means are provided for cyclically pivoting said thread catcher from an at rest position beyond the eye of the looper past the looper butt so as to seize the needle and looper threads and cut same and to return the thread catcher to its at rest position while thread retaining means retains a length of said looper thread at the ledger blade.

United States Patent Ciecior et al.

[4 1 Feb, 25, 1975 UNDERBED THREAD TRIMMER FOR Cll-IAINSTITCH SEWING MACHINES [75] Inventors: Heinrich Ciecior, Ettlingen; Rolf E.

Kessler, Karlsruhe, both of Germany [73] Assignee: The Singer Company, New York,

[22] Filed: May 9, 1974 [21] App]. No.2 468,630

52 vs. C]. 1112/252 [51] Int. Cl D05b 65/02 [58] Field of Search 112/252, 252.5, 253, 129, 112/130 {56] References Cited UNITED STATES PATENTS 3,405,672 10/1968 Ross 112/252 3,424,117 l/1969 112/252 3,554,149 1/1971 Diehm et al. 112/252 3,602,170 8/1971 Sakashita 1112/252 3,658,021 4/1972 Hedegaard et a1 112/252 3,688,716 9/1972 Heimann et a1. 112/252 3,709,176 1/1973 Papajewski et al. 112/252 3,776,161 12/1973 Papajewski et al. 112/252 [57] ABSTRACT An underbed thread trimmer for a chainstitch sewing machine in which a pair of ledger blades are adjustably mounted on the machine bed, a thread catcher being carried pivotably by said bed having needle thread and looper thread catching hooks and a pair of cutting edges cooperable with respective ones of said ledger blades. Means are provided for cyclically pivoting said thread catcher from an at rest position beyond the eye of the looper past the looper butt so as to seize the needle and looper threads and cut same and to return the thread catcher to its at rest position while thread retaining means retains a length of said looper thread at the ledger blade.

10 Claims, 9 Drawing Figures mamawz 1867,892-

sumeg g UNDERBED THREAD TRIMMER FOR CHAINSTITCH SEWING MACHINES BACKGROUND OF THE INVENTION Underbed thread trimmers for sewing machines are well known. It has likewise been known heretofore that in the formation of chain stitches it is desirable, subsequent to the cutting of the needle and looper threads, to retain the remaining looper thread so as to afford a sufficient length of such thread to begin the next stitch whereby upon descent of the needle it can penetrate the triangle formed in part by the looper thread which extends from the eye of the looper and in part by the needle thread from the preceding stitch. Unless the looper thread is claimed or otherwise prevented from pulling out of the looper eye the proper formation of the next stitch becomes uncertain.

Various chainstitch thread trimming or cut-off devices have been employed; however, the need still exists for a simple yet reliable thread trimmer. One commonly used prior device employs a reciprocable thread catcher with a pair of thread catching hooks, one of the hooks catching the needle thread and the other of such hooks catching the looper thread on the forward stroke of the thread catcher towards the eye of the looper from the butt end thereof, the return reciprocation of the thread catcher carrying both needle and looper threads into engagement with a cutting blade. It is also known to utilize with such a device a spring clip which, in cooperation with the looper thread catching hook, clamps the looper thread followed by cutting of the threads. The thread catcher and/or the spring clip must be specially formed in order to provide for clamping of only the looper thread. In such devices, where reciprocation of the thread catcher is necessary to first seize the needle and looper threads and then transport such threads to the cutting blade, there must be precise coordination in order to effect both correct seizure and cutting ofthe threads. As wear increases the tolerances between the parts, such precision becomes less than optimum. The requirement for reciprocation of the thread catcher in order to accomplish both correct seizure and cutting of the needle and looper threads thus becomes more difficult to attain and, therefore, the need arises for a thread trimmmer which can effect the seizure and cutting steps by a less complex technique whereby there is greater assurance of reliability with increased age of the machine. Also, with prior thread trimmers of the type referred to it has been necessary to provide adequate space within the bed of the machine for positioning of the thread catcher in an at rest stage which will not interfere with the stitch forming process. The bed must also afford the necessary space requirements for the thread catcher to move sequentially into and from thread seizure and thread cutting positions. As will be readily appreciated by persons versed in the art, space is at a premium in the stitch forming area of the bed; thus, a thread trimming technique and mechanism which requires less space in the critical area of the bed would be advantageous.

SUMMARY OF THE INVENTION It is accordingly one object of the invention to provide an underbed thread trimmer for a chainstitch sewing machine by which the needle and looper threads are seized and carried to the cutting blades for trimming in a single direct movement of the thread catcher.

It is another object of the invention to provide an underbed thread trimmer for a chainstitch sewing machine by which the looper thread only is clampable during cutting and separate adjustable ledger blades are utilized whereby the length of the uncut needle and looper threads may be regulated.

A further object of the invention is to provide an underbed thread trimmer for a chainstitch sewing machine which requires less space to effectuate the thread seizing and cutting steps and for at rest storage for the thread catcher.

Yet another object of the invention is the provision of an underbed thread trimmer for a chainstitch sewing machine in which the thread catcher is stored at a point beyond the eye of the looper and is adapted to traverse beyond the other extremity of the looper to seize and trim the threads before returning to its storage position.

Other objects and advantages of the invention will become readily apparent from the following description of the invention.

According to the present invention there is provided an underbed thread trimmer for a chainstitch sewing machine, comprising a pair of ledger blades adjustably mounted on the bed of the machine, a thread catcher pivotably mounted on said bed having needle thread and looper thread engaging means and cutting edges cooperable with respective ones of said ledger blades, means for effecting cyclical pivotal movement of said thread catcher from an at rest position on one side of the sewing machine needle to a position on the other side of said needle where said. needle and looper threads are engaged and transported in the same general direction to said ledger blades for cutting, thread retaining means being provided in association with one of said ledger blades for retaining a predetermined length of looper thread prior and subsequent to cutting.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more fully comprehended it will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a top plan view of the thread trimmer of the v invention in the bed of thesewing machine illustrating,

inter alia, the relationship between the ledger blades and the throat plate of the machine;

FIG. 2 is a side elevational view, partly in crosssection, taken in the direction of line 2-2 of FIG. 1;

FIGS. 3, 4 and 5 are enlarged diagrammatic views showing the relationship between the thread retaining means, the thread catcher and the blade for trimming the looper thread in successive stages of the trimming operation;

FIG. 4 depicts the elements at the moment the thread 15 cut;

FIG. 5 shows the retaining of the thread at the ledger knife; and

FIGS. 6 through 9 are diagrammatic views showing the thread trimming operation in successive stages.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS. 1 and 2 there is shown the bed 10 of a sewing machine. Mounted on the bed of the machine, such as by mounting screws 12, is a throat plate 14 which may be of the conventional type. Also mounted on the machine bed 1.0 to one side of the throat plate are a pair of trimming knives or ledger blades l6, 18. As will be described in greater detail hereafter, one of the knives if employed to cut or trim the needle thread whereas the other of such knives is utilized in conjuction with the cutting or trimming of the looper thread. As can be seen clearly from FIG. 1, each of the knives is provided with at least one elongated slot dimensioned to receive fastening means such as screws 22 which secure the knives adjustably to the bed of the machine. Loosening of the screws thus permits longitudinal movement of the knives and thereby the length of needle or looper thread subsequent to cutting. The cutting edges of the knives are shown at 24, 26. Adjusting screws 28 are provided in the knives for adjusting the height of the cutting edges as desired.

Secured to the underside of one trimming knife is a thread retaining means 30 which comprises a leaf spring 32 connected at one end to knife 16 and looper thread nipping means in the form of a tightly wound spiral spring 34 which is secured adjacent the free end of the leaf spring such that it is spring urged towards yieldable engagement with knife 16. As will be hereinafter described, movement of a thread catcher 36 between the thread nipping means 34 and knife 16 will result in movement of the spiral spring and leaf spring away from the knife. The leaf spring 32 is longitudinally adjustable relative to the trimming knife by means of screw 38.

A bearing block 40 is carried by the front end of the bed 10 by fastening means such as screws or studs 42. Journaled rotatably in the bearing block is a control shaft 44. The upper end of the control shaft carries a crank arm 46 which may be restrained from axial displacement preferably by abutting against the bushing (not shown) within which the upper end of the control shaft is journaled. Crank arm 46 is desirably formed as a generally U-shaped or channel member, the base of the channel being dimensioned to receive a thread catcher member 36. The thread catcher may be secured fixedly to the crank arm by fastening means such as screws 50.

The lower end of control shaft 44 has a control lever 52 mounted thereon. As will be described hereafter, control lever 52 is operatively connected to means which may include a solenoid and appropriate linkage in order to provide for cyclical pivotal movement of the thread catcher in timed relation to the reciprocation of the sewing needle of the machine and the looper 76 of the machine. A clamping screw 54 secures the control lever to the control shaft and may be utilized to establish the limits for the rotational movement of the control shaft and thereby of the pivotal movement of the crank arm and thread catcher.

The lower end portion of the control lever 52 is given a socket opening dimensioned to receive one end of a ball stud member 56. The other end of the ball stud member is confined within a sleeve 58 which connects the control lever operatively to reciprocating rod 59 of means such as a double acting linear solenoid 60 which in turn is carried by the bed 10 of the machine by a bracket 62 and screws or studs 64. The solenoid may be, in any known manner, coupled to the sewing machine drive system so as to effectuate a timed actuation of sleeve 58 and consequent rotation of control lever 52, control shaft 44 and pivotal movement of crank arm 46 and thread catcher 36 in proper timed relationship to the sewing machine needle and looper.

As may be observed most clearly in FIGS. 1 and 6, the thread catcher 36 is mounted on crank arm 46 so as to pivot through an arc located beneath the plane of throat plate 14 from a storage or at rest position which is located beyond the beak of looper 76 to a position beyond the other extremity or butt of the looper to seize the needle and looper threads without having to penetrate the needle thread loop. The thread catcher, in its arc of travel, continues with the threads to the cutting edges of the knives where they are severed. The thread catcher is then returned to its at rest or storage position. It will thus be seen that in a single direct sweep the thread catcher seizes the needle and looper threads and carries them to the cutting edges of the knives where they are severed, the reciprocation of the thread catcher serving to return same to storage.

The thread catcher comprises a base section 66 dimensioned for positioning within the channel section of the crank arm and an offset portion 68 which carries at its extremity a pair of thread catching hooks 70, 72. Each of such hooks 70, 72 is formed to present an inclined cutter edge 74 which cooperate with respective ones of said cutting edges 24, 26 of the knife elements 16, 18.

The sewing machine is provided, as aforestated, with a looper 76 carrying a looper thread 80 which may be driven in known manner in timed relation to the reciprocation of a sewing machine needle 78 carrying a needle thread 84; so as to form chainstitches which comprise loops 86 of looper thread and looper 88 of needle thread passed alternately one through the other. The looper 76 as shown in the drawings includes a blade 90 which extends from a butt 92 at which the blade is attached to the looper drive mechanism to a beak 94 located at the free end of the blade beyond the thread carrying eye 96.

Referring to FIGS. 3, 4, 5, 6, 7, 8 and 9 it will be seen that as the thread catcher 36 approaches the looper 76 from its at rest position to the left of sewing machine needle 78, with the needle in its up position, one of hooks 70, 72 will seize the needle thread running from the needle hole to the looper blade whereas the other hook will seize the looper thread running from the needle hole to the eye of the looper adjacent the point of the looper. The looper thread 80 is thus carried by the thread catcher hook 70 between the thread nipping means 34 and knife 16 thereby urging the nipping means out of engagement with the knife and permitting the looper thread 80 to slip between the windings of the spiral spring 34. Continued movement of the thread catcher 36 with both the needle and looper threads causes such threads to be brought into engagement between the cutter edges of the hooks 70, 72 and the respective cutting edges of the knives. The threads are thus trimmed, leaving one severed end 98 of the looper thread running to the stitched seam and another severed end 100 running to the eye of the looper, and the thread catcher begins its traverse back to the at rest position to the left of the needle. However, as the hook 70 is retracted from between the nipping means 34 and knife 16 the leaf spring urges the spiral back into engagement with the underside of the knife and thereby retains the desired severed end 100 of looper thread. Retention of such looper thread insures against slippage of such thread through the looper eye and encourages immediate formation of a looper thread loop 86 when stitching is next commenced.

The needle thread 84 is similarly severed by the hook 72 cooperating with the knife 18 but neither severed needle thread end is nipped.

It will thus be seen that the thread catcher 36 in a single direct movement from its at rest position to the left of the needle effectuats a seizure of the needle and looper threads, cutting of both threads with retention of the desired length of looper thread before returning to its at rest position. The knives, as aforestated, are capable of simple adjustment in order to establish the desired lengths of the trimmed threads.

Numerous alterations of the structure herein disclosed will suggest themselves to those skilled in the art. However, it is to be understood that the present disclosure relates to a prefered embodiment of the invention which is for purposes of illustration only and not to be construed as a limitation of the invention. All such modifications which do not depart from the spirit of the invention are intended to be included within the scope of the appended claims.

Having thus set forth the nature of the invention, what is claimed herein is:

1. An underbed thread trimmer for a chainstitch sewing machine, comprising a pair of ledger blades adjustably mounted on the bed of the machine, a thread catcher pivotably mounted on said bed having needle thread and looper thread engaging means and cutting edges cooperable with respective ones of said ledger blades, means for effecting cyclical pivotal movement of said thread catcher from an at rest position on one side of the sewing machine needle to a position on the other side of said needle where said needle and looper threads are engaged and transported in the same general direction to said ledger blades for cutting, thread retaining means being provided in association with one of said ledger blades for retaining a predetermined length of looper thread subsequent to cutting.

2. An underbed thread trimmer according to claim 1, wherein said thread engaging means on said thread catcher comprise a pair of hook members, said thread retaining means being urged towards yielding engagement with said one ledger blade and separable therefrom by movement of one of said thread engaging hooks therebetween.

3. An underbed thread trimmer according to claim 2, wherein said thread retaining means includes a leaf spring connected at one end to said one ledger blade, a spiral spring being secured adjacent the free end of said leaf spring urged towards engagement with said one ledger blade.

4. An underbed thread trimmer according to claim 1, wherein said ledger blades are secured to said machine bed to one side of the throat plate of the machine, each of said blades being provided with at least one elongated slot and fastening means passing through said elongated slots thereby securing said blades adjustably longitudinally to said machine bed.

5. An underbed thread trimmer according to claim 1, wherein a bearing block is secured to said machine bed,

a control shaft is rotatably carried by said bearing block, a crank arm is secured to the upper end of said control shaft and the lower end of said control shaft is connected to means for cyclically rotating same in timed relationship to the reciprocation of the needle of the machine and the looper of the machine, the end of said thread catcher remote from said thread catching hooks being secured to said crank arm for pivotal movement thereby.

6. An underbed thread trimmer according to claim 5, wherein the lower end of said control shaft carries a control lever, said control lever being provided with an aperture dimensioned to receive one end of a ball stud member, the other end of said ball stud member being operatively connected to a linear double acting solenoid adapted to cyclically rotate said control lever and control shaft in predetermined timed relation to the sewing machine needle and looper.

7. An underbed thread trimmer according to claim 5, wherein said thread catcher is pivotable by said crank arm from an at rest position at the opposite side of said throat plate from that at which said ledger blades are located across said throat plate but beneath same to a position where said cutting edges are cooperable with said ledger blades and thence back to said at rest position.

8. An underbed thread trimmer according to claim 1, wherein said ledger blades are mounted in side-by-side relation, said thread catcher comprising a pair of sideby-side mounted thread catching hooks, each of said hooks having an inclined cutter edge cooperable with respective ones of said ledger blades.

9. An underbed thread trimmer according to claim 8, wherein one of said thread catching books is more forwardly disposed than the other and is located so as to seize the looper thread.

10. An underbed thread trimmer for a chainstitch sewing machine in which a looper including a blade having a beak and butt at opposed end regions thereof is driven in timed relation with the reciprocation of the needle of the machine in the formation, of chainstitches, comprising a pair of ledger blades adjustably mounted on the bed of the machine, a thread catcher pivotably mounted on said bed having needle thread and looper thread engaging means and cutting edges cooperable with respective ones of said ledger blades, means for effecting cyclical pivotal movement of said thread catcher from an at rest position beyond the beak of said looper past said beak to a point where said needle and looper threads are seized before being transported in the same general direction beyond the butt of the looper to said ledger blades where said threads are severed, said means for effecting cylical pivotal movement of said thread catcher then being adapted to return said thread catcher to its at rest position, thread retaining means being provided in association with one of said ledger blades retaining a predetermined length of longer thread subsequent to cutting. 

1. An underbed thread trimmer for a chainstitch sewing machine, comprising a pair of ledger blades adjustably mounted on the bed of the machine, a thread catcher pivotably mounted on said bed having needle thread and looper thread engaging means and cutting edges cooperable with respective ones of said ledger blades, means for effecting cyclical pivotal movement of said thread catcher from an at rest position on one side of the sewing machine needle to a position on the other side of said needle where said needle and looper threads are engaged and transported in the same general direction to said ledger blades for cutting, thread retaining means being provided in association with one of said ledger blades for retaining a predetermined length of looper thread subsequent to cutting.
 2. An underbed thread trimmer according to claim 1, wherein said thread engaging means on said thread catcher comprise a pair of hook members, said thread retaining means being urged towards yielding engagement with said one ledger blade and separable therefrom by movement of one of said thread engaging hooks therebetween.
 3. An underbed thread trimmer according to claim 2, wherein said thread retaining means includes a leaf spring connected at one end to said one ledger blade, a spiral spring being secured adjacent the free end of said leaf spring urged towards engagement with said one ledger blade.
 4. An underbed thread trimmer according to claim 1, wherein said ledger blades are secured to said machine bed to one side of the throat plate of the machine, each of said blades being provided with at least one elongated slot and fastening means passing through said elongated slots thereby securing said blades adjustably longitudinally to said machine bed.
 5. An underbed thread trimmer according to claim 1, wherein a bearing block is secured to said machine bed, a control shaft is rotatably carried by said bearing block, a crank arm is secured to the upper end of said control shaft and the lower end of said control shaft is connected to means for cyclically rotating same in timed relationship to the reciprocation of the needle of the machine and the looper of the machine, the end of said thread catcher remote from said thread catching hooks being secured to said crank arm for pivotal movement thereby.
 6. An underbed thread trimmer according to claim 5, wherein the lower end of said control shaft carries a control lever, said control lever being provided with an aperture dimensioned to receive one end of a ball stud member, the other end of said ball stud member being operatively connected to a linear double acting solenoid adapted to cyclically rotate said control lever and control shaft in predetermined timed relation to the sewing machine needle and looper.
 7. An underbed thread trimmer according to claim 5, wherein said thread catcher is pivotable by said crank arm from an at rest position at the opposite side of said throat plate from that at which said ledger blades are located across said throat plate but beneath same to a position where said cutting edges are cooperable with said ledger blades and thence back to said at rest position.
 8. An underbed thread trimmer according to claim 1, wherein said ledger blades are mounted in side-by-side relation, said thread catcher comprising a pair of side-by-side mounted thread catching hooks, each of said hooks having an inclined cutter edge cooperable with respective ones of said ledger blades.
 9. An underbed thread trimmer according to claim 8, wherein one of said thread catching hooks is more forwardly disposed than the other and is located so as to seize the looper thread.
 10. An underbed thread trimmer for a chainstitch sewing machine in which a looper including a blade having a beak and butt at opposed end regions thereof is driven in timed relation with the reciprocation of the needle of the machine in the formation, of chainstitches, comprising a pair of ledger blades adjustably mounted on the bed of the machine, a thread catcher pivotably mounted on said bed having needle thread and looper thread engaging means and cutting edges cooperable with respective ones of said ledger blades, means for effecting cyclical pivotal movement of said thread catcher from an at rest position beyond the beak of said looper past said beak to a point where said needle and looper threads are seized before being transported in the same general direction beyond the butt of the looper to said ledger blades where said threads are severed, said means for effecting cylical pivotal movement of said thread catcher then being adapted to return said thread catcher to its at rest position, thread retaining means being provided in association with one of said ledger blades retaining a predetermined length of longer thread subsequent to cutting. 